Borrowings - Long-term Debt (Details) - USD ($)	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Borrowings, carrying amount	$ 350,000,000	$ 0
Senior Notes
Debt Instrument [Line Items]
Borrowings, carrying amount	123,630,000	123,871,000
Senior Subordinated Notes
Debt Instrument [Line Items]
Borrowings, carrying amount	181,115,000	108,977,000
Maturing September 2024 \| Senior Notes
Debt Instrument [Line Items]
Borrowings, carrying amount	$ 24,432,000	0
Face amount, percentage	4.50%
Issue of subordinated term note	$ 25,000,000
Senior unsecured notes aggregate amount	$ 25,000,000
Redemption price, percent of principal balance	100.00%
Maturing June 2022 \| Senior Notes
Debt Instrument [Line Items]
Borrowings, carrying amount	$ 99,198,000	98,911,000
Face amount, percentage	3.95%
Issue of subordinated term note	$ 100,000,000
Senior unsecured notes aggregate amount	$ 100,000,000
Redemption price, percent of principal balance	99.775%
Maturing June 2019 \| Senior Notes
Debt Instrument [Line Items]
Borrowings, carrying amount	$ 0	24,960,000
Face amount, percentage	4.625%
Issue of subordinated term note	$ 25,000,000
Senior unsecured notes aggregate amount	$ 25,000,000
Redemption price, percent of principal balance	100.00%
Maturing December 2034 \| Senior Subordinated Notes
Debt Instrument [Line Items]
Borrowings, carrying amount	$ 72,040,000	0
Face amount, percentage	5.375%
Issue of subordinated term note	$ 74,750,000
Senior unsecured notes aggregate amount	$ 74,750,000
Redemption price, percent of principal balance	100.00%
Maturing June 2029 \| Senior Subordinated Notes
Debt Instrument [Line Items]
Borrowings, carrying amount	$ 109,075,000	$ 108,977,000
Face amount, percentage	6.125%
Issue of subordinated term note	$ 110,000,000
Senior unsecured notes aggregate amount	$ 110,000,000
Redemption price, percent of principal balance	100.00%
London Interbank Offered Rate (LIBOR) \| Maturing June 2029 \| Senior Subordinated Notes
Debt Instrument [Line Items]
Spread on variable interest rate	3.443%

Debt Instrument, Face Amount, Percentage

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- Definition

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+ References

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- Definition

Face (par) amount of debt instrument at time of issuance.

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- Definition

Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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